Download or read book Influence of Flexoelectric Effect on Director Alignment of Nematic Liquid Crystals in Axial Arrangement Cylindrical Cells written by and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract : A positive nematic liquid crystal (5CB) sample is confined in cylindrical cells under strong or weak axial anchoring boundary conditions when a radial nonuniform low-frequency electric field is applied and the flexoelectric effect is taken into account. Based on the Frank elastic free energy, the surface energy of the Rapini–Papoular approximation, the polarization free energy and the flexoelectric free energy caused by electric field, we obtain the free energy density of the nematic and solve the corresponding Euler–Lagrange equation numerically. We investigate the director distribution, the critical voltage and the critical exponent of nematic liquid crystal in cylindrical cells. It follows that the critical exponent is the classical one. It is also shown that the critical voltage in the system is affected by the flexoelectric effect, the geometric effect and radial weak anchoring effect on the cylindrical surfaces. A new type of director transition caused by the flexoelectric effect, the dielectric coupling effect and the radial weak anchoring effect is found.

Download or read book Flexoelectricity in Liquid Crystals written by Agnes Buka and published by World Scientific. This book was released on 2013 with total page 299 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book intends to give a state-of-the-art overview of flexoelectricity, a linear physical coupling between mechanical (orientational) deformations and electric polarization, which is specific to systems with orientational order, such as liquid crystals. Chapters written by experts in the field shed light on theoretical as well as experimental aspects of research carried out since the discovery of flexoelectricity. Besides a common macroscopic (continuum) description the microscopic theory of flexoelectricity is also addressed. Electro-optic effects due to or modified by flexoelectricity as well as various (direct and indirect) measurement methods are discussed. Special emphasis is given to the role of flexoelectricity in pattern-forming instabilities. While the main focus of the book lies in flexoelectricity in nematic liquid crystals, peculiarities of other mesophases (bent-core systems, cholesterics, and smectics) are also reviewed. Flexoelectricity has relevance to biological (living) systems and can also offer possibilities for technical applications. The basics of these two interdisciplinary fields are also summarized.

Download or read book Electrooptic Effects in Liquid Crystal Materials written by L.M. Blinov and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 477 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electrooptic effects provide the basis for much liquid-crystal display technology. This book, by two of the leaders in liquid-crystal research in Russia, presents a complete and accessible treatment of virtually all known phenomena occurring in liquid crystals under the influence of electric fields.

Download or read book Surfaces and Interfaces of Liquid Crystals written by Igor Muševič and published by Springer Science & Business Media. This book was released on 2004-08-11 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book describes the state of the art of our understanding of liquid-crystal interfaces on a molecular level. The interactions of liquid crystal molecules with a surface play an essential role in the operation of liquid crystal displays (LCD's) and other LC devices that are based on the controllable anchoring of LC molecules on polymer coated surfaces. This book addresses the microscopic interaction between a macromolecule (liquid crystal, polymer) and a wall, using state of the art surface and interface-sensitive experimental techniques, such as Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), Linear and Nonlinear Optical Microscopy and (Dynamic) Light Scattering (DLS). These experimental techniques were complemented with computer simulations and supra molecular chemistry methods to develop controllable polymeric surfaces.

Download or read book Flexoelectric Liquid Crystals and Their Applications written by Yingfei Jiang and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Liquid crystals are widely used in flat panel displays and smart windows. In flat panel display application, one way to improve the efficiency is to decrease the driving frequency when static images are displayed. As the driving frequency is decreased, the transmittance of the display may vary with time, a phenomenon known as flickering. We carried out both experimental and simulation studies to investigate the origins that cause the flickering problem. Our results show that flexoelectric effect and ions in the liquid crystal are the main factors responsible for the flickering. We quantitatively analyzed the flickering caused by the two factors. The ionic effect can be eliminated by using the fluorinated liquid crystals with high resistivity. The flexoelectric effect is attributed to the intrinsic flexoelectric coefficient of the liquid crystal and nonuniformity of the liquid crystal director configurations. We demonstrated that polymer stabilization can smooth the spatial variation of the liquid crystal orientation, while doping a liquid crystal dimer can reduce the flexoelectric coefficient of the liquid crystal. Using these methods we are able to reduce the flickering significantly. Radiant energy-flow control and privacy control are two important features for smart windows (or glass). Current smart window technologies can, however, only control one of them: radiant energy flow or privacy. Therefore, a dual-mode smart window is highly desirable. We developed a dual-mode switchable liquid-crystal window that can control both radiant energy flow and privacy. The switchable liquid-crystal window makes use of dielectric and flexoelectric effects. In the absence of an applied voltage, the window is clear and transparent, and radiant energy can flow through it and the scenery behind the window can be seen. When a low-frequency (50 Hz) voltage is applied, the window is switched to an optical scattering and absorbing state by a flexoelectric effect, and thus, privacy is protected. When a high-frequency (1 kHz) voltage is applied, the window is switched to an optical absorbing but nonscattering state through a dielectric effect, and thus, radiant energy flow is controlled. Smart windows can be categorized mainly into two types according to the operation principle: electrical switchable window and thermal switchable windows. In the electric switchable window, voltage must be applied to switch the window, which consumes energy and is not environmentally friendly. Therefore, a power-free smart window is highly demanded. We developed a thermal switchable smart window that is sensitive to ambient temperature. The window is based on a liquid crystal whose orientation imposed by an alignment layer varies with temperature. The liquid crystal layer is sandwiched between two parallel polarizers to make the window. At high temperature, the liquid crystal is aligned parallel to the cell substrate and rotates the polarization of the incident light after the first polarizer by 90o such that incident light is completely absorbed by the second polarizer, and the transmittance of the window is 0. When temperature is decreased, the liquid crystal is tilted toward the cell substrate normal and rotates the polarization of the incident light less so that some light can pass the second polarizer, and the transmittance of the window increases. When temperature is decreased below a critical value, the liquid crystal is aligned perpendicular to the cell substrate and does not rotate the polarization of the incident light such that all light passes the second polarizer, and the transmittance reaches a maximum.

Download or read book Structure and Properties of Liquid Crystals written by Lev M. Blinov and published by Springer Science & Business Media. This book was released on 2010-10-26 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book by Lev M. Blinov is ideal to guide researchers from their very first encounter with liquid crystals to the level where they can perform independent experiments on liquid crystals with a thorough understanding of their behaviour also in relation to the theoretical framework. Liquid crystals can be found everywhere around us. They are used in virtually every display device, whether it is for domestic appliances of for specialized technological instruments. Their finely tunable optical properties make them suitable also for thermo-sensing and laser technologies. There are many monographs written by prominent scholars on the subject of liquid crystals. The majority of them presents the subject in great depth, sometimes focusing on a particular research aspect, and in general they require a significant level of prior knowledge. In contrast, this books aims at an audience of advanced undergraduate and graduate students in physics, chemistry and materials science. The book consists of three parts: the first part, on structure, starts from the fundamental principles underlying the structure of liquid crystals, their rich phase behaviour and the methods used to study them; the second part, on physical properties, emphasizes the influence of anisotropy on all aspects of liquid crystals behaviour; the third, focuses on electro-optics, the most important properties from the applications standpoint. This part covers only the main effects and illustrates the underlying principles in greater detail. Professor Lev M. Blinov has had a long carrier as an experimentalist. He made major contributions in the field of ferroelectric mesophases. In 1985 he received the USSR state prize for investigations of electro-optical effects in liquid crystals for spatial light modulators. In 1999 he was awarded the Frederiks medal of the Soviet Liquid Crystal Society and in 2000 he was honoured with the G. Gray silver medal of the British Liquid Crystal Society. He has held many visiting academic positions in universities and laboratories across Europe and in Japan.

Download or read book Opticals Effects in Liquid Crystals written by I. Jánossy and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt: In 1988 physicists and chemists commemorated the centenary of the discovery of the first liquid crystals. Fora long period after this discovery, although many significant results were found, liquid crystal research remained a marginal topic of condensed matter physics. The situation changed in the sixties. At that time the remarkable electro-optical properties of liquid crystals were recognized and found soon widespread application in numeric displays. From a more fundamental point of view, the interest in disordered systems. increased in general at the same time. Liquid crystals represented an important dass of such systems. Among others, phase transitions, hydrodynamics and topological defects occurring in them attracted considerable attention. The connection between the liquid-crystalline state and the structure of biological membranes stimulated a Iot of works also. In the present volume we discuss a relatively new and rapidly developing branch of the fi. eld, namely nonlinear optical effects in liquid crystals. Optical studies have always played a signifi. cant role in liquid crystal science. Research of optical nonlinearities in liquid crystals began at the end of the sixties. Since then it became a powerful tool in the investigation of symmetry properties, interfacial phenomena or dynamic behaviour. Furthermore, several new aspects of nonlinear processes were demonstrated and studied extensively in liquid crystals. The subject covered in this book is therefore of importance both for liquid crystal research and for nonlinear optics itself. The term "nonlinear optics" is used here in a broad sense.

Download or read book Alignment Technology and Applications of Liquid Crystal Devices written by Kohki Takatoh and published by CRC Press. This book was released on 2005-07-21 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: Alignment phenomena are characteristic of liquid crystalline materials, and understanding them is critically important in understanding the essential features and behavior of liquid crystals and the performance of Liquid Crystal Devices (LCDs). Furthermore, in LCD production lines, the alignment process is of practical importance. Alignment Technologies and Applications of Liquid Crystal Devices demonstrates both the fundamental and practical aspects of alignment phenomena in liquid crystals. The physical basis of alignment phenomena is first introduced in order to aid the understanding of the various physical phenomena observed in the interface between liquid crystalline materials and alignment layer surfaces. Methods for the characterization of surfaces, which induce the alignment phenomena, and of the alignment layer itself are introduced. These methods are useful for the research of liquid crystalline materials and devices in academic research as well as in industry. In the practical sections, the alignment methods used in the LCD production lines are introduced with various other trials for the alignment technologies. LCD performances are also discussed in relation to alignment phenomena. The authors have a wide range of experience in both academic research and in industry. This book will be of interest to researchers and engineers working in the LCD industry, and for physics and chemistry researchers studying liquid crystalline materials.

Download or read book Flexoelectricity in Nematic Liquid Crystals written by Claudius Kischka and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Flexoelectricity in liquid crystals is thought to be due to a coupling between dielectric properties and shape anisotropy of the molecules and described by the fiexoelectric coefficients el and e3. Two experiments are needed to measure el and e3 and it is usual to measure the difference (el - e3) and the sum (el + e3) and then calculate el and e3· The first experiment to measure the difference (el - e3) uses a TN structure with an in-plane applied electric field. Due to the dielectric coupling, the director aligns with the electric field and due to the fiexoelectric effect, the director tilts out of plane. This tilt is measured optically using two laser beams at oblique incidence, e.g. 45°. Using a theoretical model the experimental data is fitted and the difference (el - e3) extracted. The second experiment to measure the sum (el + e3) uses a Pi cell. Applying an ac voltage the transmission through the device is a repeating oscillating signal which contains 1st and 2nd harmonics. The 1st harmonic corresponds to the fiexoelectric effect and the 2nd harmonic to the dielectric effect. Using a lock-in amplifier, the harmonics were measured and the sum (el + e3) extracted using a theoretical model to fit the experimental data. Unfortunately, the data proved the experiment to be unreliable and another method was developed, which uses a BAN cell. The third experiment uses simple pulses in a BAN cell and also measures the sum (el + e3). The big disadvantage of the BAN cell is an internal voltage, which is created by the homeotropic alignment layer and the fiexoelectric polarisation. The internal voltage has the same effect on the director profile as the fiexoelectric effect, which is a big problem in measuring fiexoelectricity. Using a material, which is non ionic and has no fiexoelectricity, the internal bias could be measured and taken into account. Applying short de pulses of opposite sign, the fiexoelectric effect can be observed by the optical response and can be measured. Using these experiments, a number of investigation are being carried out such as the correlation between fiexoelectricity and the molecular structure, ions, elastic properties, molecular orientation, dielectric anisotropy 6E, and order parameter S. The results showed that fiexoelectricity only depends on ions and dielectric properties which was very interesting and surprising at the same time.

Download or read book Unconventional Liquid Crystals and Their Applications written by Wei Lee and published by Walter de Gruyter GmbH & Co KG. This book was released on 2021-07-19 with total page 738 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work focuses on recent developments of the rapidly evolving field of Non-conventional Liquid Crystals. After a concise introduction it discusses the most promising research such as biosensing, elastomers, polymer films , photoresponsive properties and energy harvesting. Besides future applications it discusses as well potential frontiers in LC science and technology.

Download or read book Effects of Dielectric Relaxation on Director Dynamics in Uniaxial Nematic Liquid Crystals written by Mingxia Gu and published by . This book was released on 2009 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: Director reorientation dynamics is essential to most of today's liquid crystal technologies. Advances in research have allowed one to reduce the response times from millisecond to microsecond and even to nanoseconds. For these small time scales, the description of the director dynamics requires a proper account of the dielectric dispersion effects. However, the first analysis of the role of dielectric dispersion in the director dynamics has been performed only very recently. Previous investigations were limited to dual frequency nematic liquid crystals, and considered only a single dielectric relaxation process. In this thesis, we lift these limitations and propose a model that accounts for multiple processes of dielectric relaxations in both parallel and perpendicular dielectric permittivities. The model yields a number of counterintuitive predictions such as the polar contribution to the dielectric coupling between the field and the nematic liquid crystal. The most important results are summarized below: First, we developed a general model to describe the director orientation dynamics of nematic liquid crystals under an applied electric field that accounts for multiple dielectric relaxations in both parallel and perpendicular dielectric permittivities. This model presents the contribution of dielectric relaxation as a "memory" effect; the director dynamics depends not only on the present electric and director fields, but also on their pre-histories. Second, we discovered an unusual contribution to the dielectric torque as a result of dielectric memory effect. This torque is linear in the present applied electric field and is thus sensitive to its polarity. The phenomenon is accompanied by a spectacular but counter-intuitive effect: the director relaxation during the "switch-off" stage can be accelerated if instead of an abrupt vertical back edge of the voltage pulse, we apply a pulse with a non-instantaneously vanishing back edge. Third, we demonstrate the director dynamics under different "shapes" of the front edge of the voltage pulses, taking into account the dielectric relaxation. Our model allows us to optimize the front edge of the pulse to improve switching efficiency. Finally, we studied the dynamics of electrically induced isotropic-nematic (I-N) phase transition by accounting for the finite rate of the polarization dynamics, which has previously been considered an instantaneous process in the classic theory. Consequently the electrically induced nematic order parameter does not interact directly with the applied electric field, but is mediated by the dynamics of polarization. We present a model based on the Langevin equation that describes the dynamics of two crucial parameters: the polar and non-polar order parameters during the electrically induced I-N phase transition.

Download or read book Chirality effects in thermotropic and lyotropic nematic liquid crystals under confined geometries written by Clarissa Dietrich and published by Cuvillier Verlag. This book was released on 2019-12-09 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chirality is a phenomenon in nature that appears across all disciplines of natural science, from biology to mathematics. The spontaneous formation of chiral structures in a system of achiral components is known as spontaneous mirror symmetry breaking and is by itself of fundamental interest leading also towards the question of the origin of homochirality in nature in general. In this work, we show that by means of the topology imposed by the confining geometry and by interfacial boundary conditions – in combination with the physical properties of a liquid crystal – spontaneous mirror symmetry broken structures can be obtained. They are analyzed, inter alia, with respect to the types of geometrical confinements used, e.g. how the confinement amplifies, induces, and influences the detection of chirality effects in order to facilitate the measurement of tiny amounts of chiral additives qualitatively and quantitatively.

Download or read book Continuously Controllable Rotation of the Molecular Director in Ferroelectric Liquid Crystals written by Richard A. Hill and published by . This book was released on 1991 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Anomalous Alignment and electrohydrdynamic effects in nematic liquid crystals written by and published by . This book was released on 1977 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Anomalous Alignment and Electrohydrodynamic Effects in Nematic Liquid Crystals written by William Thomas Flint and published by . This book was released on 1976 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Selected Papers on Liquid Crystals for Optics written by Stephen D. Jacobs and published by . This book was released on 1992 with total page 736 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Flow Effects in Bistable Nematic Liquid Crystal Devices written by Matthew Neilson and published by . This book was released on 2008 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: We consider a nematic liquid crystal device in which a bistable surface anchoring term produces two stable states, a Vertical State (i. e. all molecules are homeotropically aligned) and a Hybrid Aligned Nematic (HAN) State (i. e. the molecules are homeotropically aligned on one boundary and homogeneously aligned on the other). Our one-dimensional model determines the director profile throughout a nematic cell by minimizing its free energy. The free energy in this model contains dielectric, elastic, flexoelectric and anchoring terms. This constitutes what we denote the 'no-flow' model. An expanded, so-called 'flow model', also includes a flow equation that we couple with our system of director equations. We then introduce three time integration methods for our numerical simulations, namely an explicit method, a semi-implicit method and a fully-implicit method, each of which employs an adaptive time-stepping algorithm to control the size of each time-step. Numerical simulations also employ a moving mesh algorithm to control the positioning and quantity of node points used at each time-step. We then compare each simulation method to determine which provides the optimal balance of speed and accuracy. We investigate switching for voltage pulses of different magnitude and duration in order to graph standard rV-plots. Each switching region is determined by the interaction between the bistable surface and bulk equations once the applied voltage is removed, which is a relatively complex process. We develop and present a powerful algorithm for automatically generating rV-plots corresponding to any given parameter set. Using this algorithm, we then investigate the effect of each parameter on the switching characteristics of our cell, using both the standard model and the expanded 'flow' model. The effects of flow are investigated by comparing the results of each model via numerical simulation. We show that flow-induced kickback in the director can significantly affect the results obtained using a no-flow model.